As a conventional chemical heat storage device, for example, a device described in Patent Literature 1 has been known. The device described in Patent Literature 1 includes a heat accumulator (reactor) which heats an oxidation catalyst provided in an exhaust system of an internal combustion engine. In the chemical heat storage device, when heating the oxidation catalyst, by supplying ammonia as a reactive medium to the reactor, the heat storage material contained in the reactor is made to chemically react with ammonia to generate heat. Further, in the chemical heat storage device, in order to suppress the thermal decomposition of ammonia in the reactor when the oxidation catalyst reaches a high-temperature state, the oxidation catalyst is divided into a first region on an upstream side and a second region on a downstream side thereof, and the reactor is disposed around the first region having a smaller carried amount of catalyst than the second region.